The present invention relates to a bi-directional digital communication unit and more particularly to a unit for requesting the performance of services by transmitting digital data to a central computer complex for purposes of processing that data and receiving digital data from the computer complex for purposes of determining whether the request for the performed services was received. The invention is particularly useful in conjunction with a community antenna system or cable television signal distribution system.
In a cable television system the television program signals are distributed to the various customers by way of a coaxial system. While such systems generally perform in a satisfactory manner, it would be desirable to employ the same coaxial cable for the transmission of various intelligent information to and from the users location to a central master station. The present state of the art to accomplish these tasks requires the use of a bi-directional RF cable television system. The cost of implementing a bi-directional cable television system is very high and the maintenance problems associated with it are extensive.
Typical bi-directional communication systems for performing the above noted functions are disclosed in U.S. Pat. Nos. 3,794,922 and 3,803,491, both to Osborn. These prior art devices typically perform bi-directional digital communication by the transmission of signals in the radio frequency range in the order of 3 megahertz to 300 megahertz. The signals which these devices receive must be decoded using filter circuits and the decoding is done by highly complex circuitry which causes such systems to be expensive. Furthermore, such devices typically do not have any means to notify the user that the central computer has received the data transmitted from the unit. In addition, such systems do not have auxiliary power supplies to provide power if the main power supply fails and correspondingly, they do not have any means to inform the central computer that the main power supply has failed.